|LADSPA (Linux Audio Developers Simple Plug-in API) is an audio plug-in standard originally developed on Linux, but which can be ported to Windows and Mac too. Audacity has built-in support for LADSPA plug-ins.
Writing LADPSA plug-ins
Audacity behaves as an excellent LADSPA host. Just read up about LADSPA, and make your plug-ins correctly. As a starting point, look at the LADSPA developers' documentation and the LADSPA site's example plug-ins. Keep in mind that Audacity "runs" the plug-in multiple times with some specific number of samples. So, don't assume that your plug-in will get the entire selection the first time. Here is an example LADSPA plug-in made by a user for plotting frequency variation.
Using LADSPA plug-ins
For instructions on how to load new Ladspa effects into Audacity please see this page in the Manual.
If you have the ladspa-sdk installed, you can run listplug-ins from a terminal to list all plug-ins in your LADSPA_PATH.
Windows and Mac OS
Audacity also supports LADSPA plug-ins on Windows and Mac OS. Any LADSPA plug-in compiled as a Windows .dll or Mac .dylib shared library will work on these platforms. An extensive set of LADSPA plug-ins is available for Windows and Mac OS X.
To add LADSPA plug-ins to Audacity, place them in the "Plug-Ins" folder inside the Audacity installation folder. Restart Audacity and the plug-ins should be in the C:\Program Files on Windows, or under Mac Hard Disk > Applications on OS X.menu, underneath the divider. The Audacity installation folder is usually under
As on Linux, Audacity will also detect LADSPA plug-ins if you put them in a folder specified in the LADSPA_PATH environment variable.